package com.example.springtest.utils;

import java.util.Stack;

public class mathcal {
    
    public static int mathcal(String expression) {
        Stack<Integer> operandStack = new Stack<>();
        Stack<Character> operatorStack = new Stack<>();
        expression = insertBlanks(expression);
        String[] tokens = expression.split(" ");

        for (String token : tokens) {
            if (token.length() == 0)
                continue;
            else if (token.charAt(0) == '+' || token.charAt(0) == '-') {
                while (!operatorStack.isEmpty() &&
                        (operatorStack.peek() == '+' ||
                                operatorStack.peek() == '-' ||
                                operatorStack.peek() == '*' ||
                                operatorStack.peek() == '/')) {
                    processAnOperator(operandStack, operatorStack);

                }
                operatorStack.push(token.charAt(0));
            } else if (token.charAt(0) == '*' || token.charAt(0) == '/') {
                while (!operatorStack.isEmpty() &&
                        (operatorStack.peek() == '*' ||
                                operatorStack.peek() == '/')) {
                    processAnOperator(operandStack, operatorStack);

                }
                operatorStack.push(token.charAt(0));
            } else if (token.trim().charAt(0) == '(')
                operatorStack.push('(');
            else if (token.trim().charAt(0) == ')') {
                while (operatorStack.peek() != '(') {
                    processAnOperator(operandStack, operatorStack);
                }
                operatorStack.pop();
            } else {
                operandStack.push(new Integer(token));
            }

        }
        while (!operatorStack.isEmpty()) {
            processAnOperator(operandStack, operatorStack);
        }
        return operandStack.pop();
    }

    private static void processAnOperator(Stack<Integer> operandStack, Stack<Character> operatorStack) {
        // TODO Auto-generated method stub
        char op = operatorStack.pop();
        int op1 = operandStack.pop();
        int op2 = operandStack.pop();
        if (op == '+')
            operandStack.push(op2 + op1);
        else if (op == '-')
            operandStack.push(op2 - op1);
        else if (op == '*')
            operandStack.push(op2 * op1);
        else if (op == '/')
            operandStack.push(op2 / op1);
    }

    private static String insertBlanks(String s) {
        // TODO Auto-generated method stub
        String result = "";
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '(' || s.charAt(i) == ')' ||
                    s.charAt(i) == '+' || s.charAt(i) == '-'
                    || s.charAt(i) == '*' || s.charAt(i) == '/')
                result += " " + s.charAt(i) + " ";
            else
                result += s.charAt(i);
        }
        System.out.println(result);
        return result;

    }
}
